use ssh paths from tugboat file

my ssh key is ~/.ssh/id_rsa and is named 'trimix' on digital ocean.

trying to find ~/.ssh/trimix[.pem] won't work for me.

could be generalized more, but i'm not super familiar with this code...
Merge remote-tracking branch 'origin/lcg/use-ssh-paths'

Conflicts:
	lib/chef_metal_fog/fog_driver.rb
Fix typo from provider split-up patch